As an SSC receiver, there are known those described e.g. in JP-B-64-11178 and U.S. patent application Ser. No. 256,394 filed Oct. 7, 1988 (now U.S. Pat. No. 4,943,975).
Between those described above, it is that described in the latter U.S. patent application, which the present invention relates to. In an SSC receiver according to this system, in which desired information is restored by means of a correlator forming the correlation between a received pseudo noise (hereinbelow abbreviated to PN) code included in a received signal and a reference PN code included in a reference signal generated on the receiver side, the output of the correlator stated above is inputted in pattern judging means and the operation of the initial synchronization for setting correctly the position, where the two codes described above are in accordance with each other, is effected by controlling the phase of the reference PN code by using the output, obtained when the output of the correlator is in accordance with a predetermined judgment pattern.
Further sampling pulses are generated in time before and after a correlation pulse produced by a correlation spike outputted by the correlator describe above. In this way, the correlation pulse is sampled and the direction and the amount of the deviation are detected. The phase of the reference PN code is controlled by using a phase control pulse corresponding to them so as to hold the two codes stated above in synchronism. The data are restored by extracting the correlation pulse in a period from the rising edge of the sampling pulse preceding in time to the falling edge of the sampling pulse succeeding in time between these two sampling pulses described above.
However this technique has a drawback that the operation of the initial synchronization is not effected, until the quality of the electromagnetic wave propagation path is restored, when the quality of the electromagnetic wave propagation path is worsened and it is difficult to make the output of the correlation be in accordance with the predetermined judgment pattern stated above, because the predetermined judgment pattern is fixed.
Further, in the case where errors in the code clock frequency of the two codes are remarkable, the correlation pulse has a tendency to be deviated towards either one of the two sampling pulses. Consequently the technique described above has another problem that the extraction between the two sampling pulses becomes unstable.